Archive for the ‘Research Paper’ Category

Polymerizing Thick Sections of BISGMA and TEGDMA

Monday, May 23rd, 2011
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Efficiency of 4,4′-bis(N,N-diethylamino) benzophenone for the polymerization of dimethacrylate resins in thick sections

Walter F Schroeder, Silvana L Asmussen, Wayne D Cook, Claudia I Vallo

Abstract

The efficiency of 4,4′-bis(N,N-diethylamino)benzophenone (DEABP) for the polymerization of dimethacrylate monomers in thick sections (12 mm) was studied. DEABP (λmax = 365 nm) represents a complete initiating system as it contains both ketone and amine functional groups. During irradiation, DEABP photobleaches at a fast rate causing deeper penetration of light through the underlying layers, but the photoinitiation efficiency (rate of polymerization per photon absorption rate) is relatively poor. As a result, irradiation of methacrylate monomers at 365 nm results in a slow average polymerization rate and a reduced monomer conversion for thick sections due to the light attenuation caused by the high absorptivity of DEABP and photolysis products. These results highlight the inherent interlinking of light attenuation and photobleaching rate in polymerization of thick sections.

Materials

The resins were formulated from blends of 2,2-bis[4-(2-hydroxy-3-
methacryloxyprop-1-oxy)phenyl]propane (bis-GMA)
and triethylene glycol dimethacrylate (TEGDMA) at mass fraction of 70:30.

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Reduced Shrinkage Stress with Optimized BisGMA/TEGDMA Ratios

Thursday, May 5th, 2011
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BisGMA/TEGDMA ratio and filler content effects on shrinkage stress

Flávia Gonçalve, Caio L.N. Azevedo, Jack L. Ferracane,Roberto R. Braga
Dental Materials, Volume 27, Issue 6, Pages 520-526 (June 2011)

Abstract

Objective

To investigate the contributions of BisGMA:TEGDMA and filler content on polymerization stress, along with the influence of variables associated with stress development, namely, degree of conversion, reaction rate, shrinkage, elastic modulus and loss tangent for a series of experimental dental composites.

Methods

Twenty formulations with BisGMA:TEGDMA ratios of 3:7, 4:6, 5:5, 6:4 and 7:3 and barium glass filler levels of 40, 50, 60 or 70wt% were studied. Polymerization stress was determined in a tensilometer, inserting the composite between acrylic rods fixed to clamps of a universal test machine and dividing the maximum load recorded by the rods cross-sectional area. Conversion and reaction rate were determined by infra-red spectroscopy. Shrinkage was measured by mercury dilatometer. Modulus was obtained by three-point bending. Loss tangent was determined by dynamic nanoindentation. Regression analyses were performed to estimate the effect of organic and inorganic contents on each studied variable, while a stepwise forward regression identified significant variables for polymerization stress.

Results

All variables showed dependence on inorganic concentration and monomeric content. The resin matrix showed a stronger influence on polymerization stress, conversion and reaction rate, whereas filler fraction showed a stronger influence on shrinkage, modulus and loss tangent. Shrinkage and conversion were significantly related to polymerization stress.

Significance

Both the inorganic filler concentration and monomeric content affect polymerization stress, but the stronger influence of the resin matrix suggests that it may be possible to reduce stress by modifying resin composition without sacrificing filler content. The main challenge is to develop formulations with low shrinkage without sacrificing degree of conversion.

LINK:  http://www.demajournal.com/article/S0109-5641%2811%2900020-0/abstract


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BisGMA – UDMA Composite with Nanosilica Fibers

Tuesday, March 29th, 2011
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Synthesis of Nanosilica Fillers for Experimental Dental Nanocomposites and Their Characterisations
Tuan Noraihan Azila Tuan Rahim1, Dasmawati Mohamad1*, Abdul Rashid Ismail1 and Hazizan Md Akil2

1School of Dental Sciences, Universiti Sains Malaysia,
2School of Material and Mineral Resources Engineering, Universiti Sains Malaysia

MATERIALS:

Tetraethyorthosilicate (TEOS), absolute ethanol, ammonia,  γ-methacryloxypropyl-trimethoxysilane (γ-MPS), acetic acid (CH3COOH), bisphenol A glycidyl methacrylate (BisGMA, Esstech), diurethane dimethacrylate (UDMA), triethylene glycol dimethacrylate (TEGDMA), camphorquinone (CQ), (2-dimethylaminoethyl) methacrylate (DMAEMA) and distilled water were used in this work. The chemicals were employed without any further purification.

ABSTRACT:

The aim of this study was to synthesise nanosilica fillers for use in the fabrication of experimental dental nanocomposites and to evaluate their properties,  including surface and mechanical properties. Monodispersed, spherical silica nanoparticles were synthesised via a sol-gel process, and a size range of 10–20 nm was obtained. Surface treatment of the nanosilica was carried out with the silane coupling agent γ-methacryloxypropyltrimethoxysilane (MPS) to reduce agglomeration of nanosilica. Experimental dental nanocomposites with two different filler contents, 30 and 35 wt%, were fabricated and polymerised with a light curing unit for 40 s. The surface morphology, surface roughness, flexural strength and elastic modulus were evaluated and compared. A nanocomposite with 35% filler content showed higher filler compaction, lower surface roughness and higher elastic modulus than a nanocomposite filled with 30% filler. However, the nanocomposite filled with 30% filler content showed higher flexural strength. Based on the results obtained, the synthesised nanosilica is a promising material for the fabrication of dental nanocomposites for tooth-filling applications.



LINK:  http://web.usm.my/jps/22-1-11/22.1.6.pdf


Journal of Physical Science, Vol. 22(1), 93–105, 2011
© Penerbit Universiti Sains Malaysia, 2011

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BISGMA & TEGDMA Form Polymer Matrix of Montmorillonite Nanocomposites

Monday, March 7th, 2011
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Preparation and characterization of light-cured methacrylate/montmorillonite nanocomposites

Veronica Mucci, Javier Perez, Claudia I Vallo


ABSTRACT

Polymer/clay nanocomposites were prepared from dimethacrylate monomers, commonly used in dental restorative resins, and an organically modified silicate (montmorillonite). The photopolymerization process was hardly affected by the presence of the silicate filler, and thus 2 mm thick samples containing 3 wt% clay were extensively cured. Transmission electron microscopy revealed that the montmorillonite platelets were either intercalated or exfoliated. Nevertheless, for all formulations, intermediate-sized aggregates of about 1 µm were present and their fraction increased as the amount of filler increased. The presence of the clay was found to have no major effect on the flexural modulus and compressive yield strength of the nanocomposites. Moreover, the water uptake of nanocomposites containing 3 wt% clay was about 10–15% higher than that of unfilled monomers. Modification of the clay surface with alternative organic cations is certainly necessary in order to achieve an optimal dispersion of the clay in the polymer matrix.

The methacrylate monomers used for the preparation of the nanocomposites were 2,2-bis[4-(2-methacryloxyethoxy)phenyl]pro-pane  (BisEMA; from Esstech, Essington, PA), triethylene glycoldimethacrylate and 1,6-bis(meth-acrylyloxy-


Article first published online: 14 OCT 2010.  DOI: 10.1002/pi.2935.  Copyright © 2010 Society of Chemical Industry

LINK:  http://onlinelibrary.wiley.com/doi/10.1002/pi.2935/full


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Properties of UDMA and Bis-GMA based Composites

Monday, February 28th, 2011
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Hydrogen bonding interactions in methacrylate monomers and polymers

Marianela T. Lemon, Melissa S. Jones, Jeffrey W. Stansbury
Department of Craniofacial Biology, University of Colorado School of Dentistry, Aurora, Colorado 80045

ABSTRACT

It is well appreciated that hydrogen bonding affects a variety of monomer and polymer properties. This study focused on Bis-GMA and urethane dimethacrylate (UDMA) to help elucidate how the strength and nature of
specific noncovalent interactions involved with these different functional dimethacrylate structures are expressed in the monomers and polymers. Hydrogen bonding interactions in monomers and comonomer mixtures as well as in appropriate model compounds were examined by FT-IR under ambient conditions, at elevated temperatures and in dilution studies. The investigation of hydrogen bonding extended to monomer viscosity, photopolymerization reaction kinetics, and polymer mechanical properties.

CONCLUSION

The strength of hydrogen bonding was shown not only to be greater for Bis-GMA compared with UDMA, but there is also greater contribution from intermolecular interactions that enhance the hydrogen bonding effects. While UDMA-based polymers reach significantly higher levels of conversion compared with Bis-GMA materials, the stronger hydrogen bonding reinforcement associated with Bis-GMA appears to provide for comparable mechanical strength properties. Depending on the hydrogen bond donor functionality of a monomer as well as its neighboring functional groups, overall monomer structure and comonomers used, hydrogen bonding can favorably affect polymerization reactivity and mechanical properties, even in materials that form highly crosslinked polymeric networks.


Wiley Periodicals, Inc. J Biomed Mater Res 83A: 734–746,2007

Link:  http://onlinelibrary.wiley.com/doi/10.1002/jbm.a.31448/abstract



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Esstech’s TEGDMA Incorporated in Hydrogel Synthesis Patent

Tuesday, February 22nd, 2011
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Forming Clear, wettable silicone hydrogel articles without surface treatments

Document Type and Number: Kind Code:  A1
Inventors: Vanderlaan, Douglas C. (Jacksonville, FL, US), Petisce, James R. (San Diego, CA, US), Alli, Azaam (Jacksonville, FL, US), Mccabe, Kevin P. (St. Augustine Beach, FL, US)
ABSTRACT

The present invention is a composition, which may be used to form contact lenses, comprising at least one silicone containing component, at least one hydrophilic component, at least one high molecular weight hydrophilic polymer and at least one diluent with an alpha value of about 0.5 to about 1 and a Hansen solubility parameter of less than about 10.
…Some of the diluents from Example 1 were used to make contact lenses from the monomer mix shown in Table 3…
TABLE 3
Component level (wt)
DMA 31%
PVP (K90) 6%
mPDMS 1000 45%
HEMA 14.75 %
CGI-819 0.25%
TEGDMA 1.5%
Norbloc< /td> 1.5%
monomer/diluent ratio 60/40
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HEMA Incorporated in Tissue Engineering Scaffolds

Monday, January 24th, 2011
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Modification of polymer networks with bone sialoprotein promotes cell attachment and spreading

Wailen D. Chan, Harvey A. Goldberg, Graeme K. Hunter, S. J. Dixon,  Amin S. Rizkalla, Journal of Biomedical Materials Research Part A

ABSTRACT:

Biomaterials used for tissue engineering scaffolds act as temporary substrates, on which cells deposit newly synthesized extracellular matrix. In cartilage tissue engineering, polycaprolactone/poly(2-hydroxyethyl methacrylate) (PCL/pHEMA) polymer blends have been used as scaffold materials, but their use in osseous tissue engineering has been more limited. The objective of this study was to evaluate modification of PCL/pHEMA surfaces with bone sialoprotein (BSP), an extracellular matrix protein important in regulating osseous tissue formation. Modification of surfaces with BSP significantly enhanced osteoblastic cell attachment and spreading, without compromising proliferation. Thus, BSP-immobilization may be a useful strategy for optimizing scaffolds for skeletal tissue engineering.

INTRODUCTION:

Tissue regeneration requires a substrate that allows cells to adhere, proliferate, and eventually form their own matrix. Polymers from the polyester family, such as poly(lactic acid), poly(glycolic acid), or their copolymers, have been the most commonly used materials to fabricate scaffolds for skeletal tissue engineering applications.  More recently, another member of this family, poly(ε-caprolactone) (PCL) has also been considered for skeletal tissue engineering. Human primary osteoblasts demonstrate attachment and spreading on PCL surfaces.

Poly(2-hydroxyethyl methacrylate) (pHEMA) is another polymer that has been used extensively as a biomaterial in drug delivery and soft-tissue applications. pHEMA gels have a propensity to calcify after prolonged implantation periods, leading to the suggestion that pHEMA could be used for filling bone or dental defects…

PREPARATION:

PCL/pHEMA semi-interpenetrating networks (sIPN’s) were prepared by combining HEMA monomer (Esstech, Essington, PA), a low-molecular-weight PCL (CAPA 2302, 3000 g/mol; Solvay Interox, Warrington, UK), and a high-molecular-weight PCL (CAPA 6506, 50,000 g/mol; Solvay Interox) in a 5.5:2.5:1 weight ratio, respectively. PCL and HEMA monomer were mixed together and placed in an oven at 60oC to facilitate melting and dissolution of PCL in HEMA monomer. After melting, the compositions were thoroughly mixed to ensure a homogenous distribution. Camphorquinone (Esstech) was added to the mixtures at 0.2% by weight of HEMA monomer. The mixtures were sonicated for approximately 8 min to evenly dissolve the camphorquinone. 1 mL polypropylene syringes (∼4 mm internal diameter) were subsequently filled with PCL/HEMA monomer compositions and cured using a Triad 2000 light-curing system (Dentsply, York, PA).


Article first published online: 31 MAR 2010, DOI:  10.1002/jbm.a.32715, Copyright 2010 Wiley Periodicals, Inc.

Volume 94A, Issue 3, pages 945–952, 1 September 2010

Link:  http://onlinelibrary.wiley.com/doi/10.1002/jbm.a.32715/abstract


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4-META Improves Adhesion in Bonding Systems

Monday, January 17th, 2011
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Effect of etchant variation on wet and dry dentin bonding primed with 4-META/acetone

N. Nakabayashi, K. Hiranuma

In the paper referenced, a 4-META based adhesive proves effective in improving monomer impregnation of demineralized dentin resulting in improved adhesion.

Abstract

Objective: To collect data that explains the advantage, if any, of wet bonding versus dry bonding to dentin, and to more clearly understand the mechanism of wet bonding.

Methods: Bovine dentin samples were prepared with #600-grit paper and were divided into four groups of six each. The first six specimens were etched with 10% citric acid and 3% ferric chloride for 10s then rinsed and blot-dried (Gr. 1: 10-3:W). The second six were etched with 10% citric acid and 3% ferric chloride then rinsed and air-dried (Gr. 2: 10-3:D). The third six were etched with 10% citric acid for 10s, rinsed and blot-dried (Gr. 3: 10-0:W). The fourth group of six samples was etched, rinsed and air-dried (Gr. 4: 10-0:D). All groups were primed with 5% 4-methacryloyloxyethyl trimellitate anhydride (4-META) in acetone for 60s and an acrylic rod was bonded to the samples using a 4-META/methyl methacrylate (MMA)-tri-n-butyl borane (TBB) resin. The samples were fashioned into dumbbell-shaped specimens and stressed in tension until bond failure, to determine tensile bond strengths. Fractured surfaces were examined by scanning electron microscopy.

 

Significance: Effective dentin bonding depended upon the etchants employed. 10-0 etching and air-drying caused the demineralized dentin to collapse in which case wet bonding became necessary to obtain good TBS data. The specimens demineralized with 10-3 did not collapse, even when air-dried; consequently both wet and dry bonding proved effective for obtaining high tensile bond strength data.

LINK:  http://www.demajournal.com/article/S0109-5641%2800%2900017-8/abstract


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Free Download of FIT 852 Data

Thursday, December 16th, 2010
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Click on the following link for a pdf download of our IADR 2010 poster.

Physical Properties of a New Low Shrink Resin

A. JOHNSTON1, F. RUEGGEBERG2, H.R. RAWLS3, H. SLAFF1, T. BARCLIFT1, and J. DUFF1, 1Esstech Inc, Essington, PA, 2Medical College of Georgia, Augusta, GA, 3University of Texas Health Science Center at San Antonio, San Antonio, TX

Introduction:

The improvement of esthetic restorative dental composites can be pursued on many fronts. A composite is made from multiple components but, generally, it is a blend of finely ground glasses and reactive monomers.  The monomers cure to provide a continuous polymer matrix for retaining the glass.  Together they present a hard surface with the capability to survive in the oral environment.  Failure of these composites is a complex phenomenon.   While clinical failure can occur when the adhesive force between the composite and the vital dental tissue is compromised, failure also occurs when stresses overcome the cohesive strength of the continuous phase of the mixture.   Catastrophic material failure can occur as wear against complementary dentition that slowly erodes the surface.   Those cracks through the polymer phase lead to composite failure.  To improve the composite properties, a new monomer has been introduced, FIT 852 Resin™, that can provide greater toughness in the polymer, greater extent of cure in the polymer, lower shrinkage stress and no change in composite material manufacture.


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PMGDM Patented as Adhesion Promoter in Nail Systems

Monday, November 8th, 2010
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METHOD OF PROMOTING ADHESION TO KERATINACEOUS SURFACE, USE OF SAME IN RESHAPING SURFACE, AND KIT THEREFOR

Inventors: George F. Cowperthwaite, Coatesville; Allen D. Johnston, West Chester, both of Pa.; Susan C. Sheariss, Swedesboro, N.J.

Assignee: Esschem, Inc., Linwood, Pa.
Appl. No.: 09/061,948

INVENTION

This invention relates to a method for improving the adhesion of monomeric and/or polymeric materials to keratinaceous substrates which substrates contain a major amount of alpha-keratin. An aspect of this invention relates to methods for reshaping essentially rigid keratinaceous surfaces such as nail plates wherein adhesion of the reshaping material is improved through the use of an adhesion promoting treatment. Still another aspect of this invention relates to a kit for nail reshaping (e.g. nail extension) which includes an adhesion-promoting composition.

A method for improving-with an adhesion-promoting composition-adhesion of a synthetic monomeric or polymeric material (such as a curable acrylic monomer/polymerized acrylic system) to a keratinaceous substrate, as in, for example, the reshaping of fingernails or toenails. The adhesion-promoting composition comprises (A) an organic, dipolar, aprotic liquid carrier and, uniformly distributed throughout said liquid carrier, (B) pyromellitic dianhydride glycerol dimethacrylate adduct (“PMGDM”). The PMGDM
isomer mixture which typically results when pyromellitic dianhydride is reacted with glycerol dimethacrylate is preferred, particularly in view of its high solubility in solvents of relatively low toxicity (e.g. lower aliphatic
ketones). The adhesion-promoting composition can, if desired, be included in a nail-reshaping kit containing the materials and implements needed to reshape the nail plate.

LINK:  http://www.freepatentsonline.com/6015549.html


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